The changing face of the Sahara

Homo erectus , 1.8-million years ago, travelled through southern Africa northwards into the Sahara, part of a larger journey that would later find this hominid in the southern Mediterranean, the Levant and Europe.

Anatomically modern humans, Homo sapiens , made similar journeys, unsuccessfully between 135,000 and 100,000 years ago, then successfully between 90,000 and 75,000 years ago. Technology and human society were on the move. It is these journeys that tell us about the changing face of the Sahara; journeys undertaken when the climate and the environment allowed. This overwhelming importance of climatology - either as a window of opportunity or as a slammed door of disaster - determined our physical and behavioural adaptations, as we focussed on surviving the struggle with our greatest enemy and sternest teacher, climate.

The Sahara has undergone several enormous variations between wet and dry due to a 41,000-year cycle in which the tilt of earth's axis changes between 22 and 24.5 degrees. Although the global situation is now more complicated, or more compromised, theoretically it is expected that, 15,000 years from now, the Sahara will be green again.

These migration routes were assumed to be northwards along the Nile river, but the lack of stone tools led scientists to search elsewhere. Stone tools have been found elsewhere in the Sahara, and radar imagery analysis has recently revealed two huge ancient rivers that had flowed through what is now desert into the Mediterranean; through a greener Sahara.

The warm, moist climate during the Holocene era - the geological epoch which began at the end of the Pleistocene 11,700 calendar years ago and continues to the present - allowed humans in the Sahara to develop from hunter gatherers to sedentary farmers. Cattle, goats and sheep were domesticated. Trade routes were numerous.

Recent excavations in an area of desert in Niger reveal fossil remains, graphically reinforced by surrounding prehistoric rock art, depicting elephants, hippos and crocodiles, which can only have signified an ancient lake. During an expedition in 2000 to the Tenere Desert in Niger, members of the Bradshaw Foundation were taken to such an extinct lake by our Tuareg guides. Prehistoric artefacts, such as arrow heads and pottery shards, were easily found on the sand, which would have been the edge of a large inland lake.

The rock art of the Sahara confirms the changing face of the Sahara, and one of the largest petroglyphs itself - the Dabous Giraffe engravings - clearly points to a greener Sahara.